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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

BORIC ACID                                         19

5.  Sulphuric and Hydrochloric Acids.—Separate portions of 1-2
c.c., diluted with 20 c.c. of water, should not be rendered turbid, even after
some hours, by barium chloride or by silver nitrate and nitric acid.

6.  Sulphurous Acid.—After treatment with barium chloride to test
for sulphuric acid, the liquid is filtered if necessary and the nitrate oxidised
with chlorine or bromine  water ; the formation of a turbidity indicates
the presence of sulphurous acid, which is oxidised to sulphuric acid and
thus precipitated by the excess of barium chloride.

7.  Empyreumatic Substances.—These are readily detected by the
smell and taste.    Small proportions are tested for by diluting 5 c.c. of the
acid with 15 c.c. of water and adding i c.c. of 0-1% permanganate solution :
the red colour should persist for 10 minutes at least.

8.  Estimation of the Acetic Acid.—In absence of other acids titration
suffices, a few grams of the acid being diluted with water and titrated with
normal potash or soda in presence of phenolphthalein;   i c.c. N-alkali =
0-060 gram of acetic acid.    When the acid contains free sulphuric and
hydrochloric acids, these must be estimated separately by the ordinary
methods.

With acetic acid containing large proportions of empyreumatic sub-
stances, Scheurer-Kestnei's method1 is employed: 20 grams of the acid
and 50 grams of phosphoric acid (15° Baume) are distilled slowly from a
glass retort. When about one-half of the liquid has distilled over, 25 c.c.
of water are added to the retort and the distillation continued until a drop
of the distillate fails to redden blue litmus paper. The acetic acid in the
distillate is then determined by means of normal soda and phenolphthalein.

BORIC   ACID

H3B03 = 62-02 (62)

This is sold in white scales (yellowish or brownish if the product is
crude) or in a crystalline powder. It dissolves in about 25 parts of cold
or 3 of boiling water, and also in alcohol or glycerine.

It may contain sulphates, alkali chlorides, ammonium salts, ferric
oxide, alumina, lime, magnesia, silica and organic substances.

1.  Insoluble  Substances.—2-3 grams are dissolved in hot water,
the insoluble matter being collected on a tared filter, washed, dried and
weighed,

2.  Silica,  Chlorides,  Sulphates.—The filtrate from the preceding
operation is acidified with nitric acid ; one part of the liquid is evaporated
to dryness for the detection of silica, and others treated with silver nitrate
and barium chloride respectively to detect chlorides and sulphates.   With
measured volumes of solution, these tests may be made quantitative.

3.  Alumina,   Iron,   Lime,   Magnesia,   Alkalies.—2-3  grams  are
evaporated to dryness with excess of pure sulphuric and hydrofluoric acids
in a platinum dish, the boric acid being thus completely ehminated as
boron fluoride.   The residue is treated with dilute hydrochloric acid and
the solution used for the detection or, if necessary, the estimation of the
iron, alumina, lime, magnesia and alkalies.

1 Butt. Soc. cMm. de Paris, 1896, XV, p. 530,nd saturating with dry, gaseous hydrogen chloride.and should be as free as possible from organic matter, nitrites, nitrates, ammonia